A resonator-fiber-optic gyroscope (RFOG) is a rotation rate measurement apparatus that uses a fiber ring resonant cavity to enhance the signal to noise ratio in the measurement of a rotation-induced Sagnac effect within the resonant cavity. The basic principle of RFOG operation is that the effective resonator path length in a clockwise (CW) and counter-clockwise (CCW) direction is different when the rotation of the fiber ring resonant cavity has a nonzero component in a resonator axis. By measuring the CW and CCW resonance frequency difference, which is proportional to Sagnac phase shift due to rotation, the RFOG can accurately measure the rotation rate.
Lasers provide coherent light to the fiber ring resonant cavity to identify its resonance frequencies. Semiconductor lasers are a low cost option for source lasers. However, semiconductor lasers typically have significant phase noise that can lead to degradation of the RFOG performance.